Amino acid identity and/or position determine the proteasomal cleavage of the HLA-A*0201-restricted peptide tumor antigen MAGE-3271-279 (original) (raw)
Related papers
Journal of Experimental Medicine, 1999
We have analyzed the presentation of human histocompatability leukocyte antigen-A*0201-associated tumor peptide antigen MAGE-3 271-279 by melanoma cells. We show that specific cytotoxic T lymphocyte (CTL)-recognizing cells transfected with a minigene encoding the preprocessed fragment MAGE-3 271-279 failed to recognize cells expressing the full length MAGE-3 protein. Digestion of synthetic peptides extended at the NH 2 or COOH terminus of MAGE-3 271-279 with purified human proteasome revealed that the generation of the COOH terminus of the antigenic peptide was impaired. Surprisingly, addition of lactacystin to purified proteasome, though partially inhibitory, resulted in the generation of the antigenic peptide. Furthermore, treatment of melanoma cells expressing the MAGE-3 protein with lactacystin resulted in efficient lysis by MAGE-3 271-279 -specific CTL. We therefore postulate that the generation of antigenic peptides by the proteasome in cells can be modulated by the selective inhibition of certain of its enzymatic activities.
The cleavage preference of the proteasome governs the yield of antigenic peptides
Journal of Experimental Medicine
Proteasomes degrade endogenous proteins in the cytosol. The potential contribution of the proteasome to the effect offlanking sequences on the presentation ofan antigenic epitope presented by the major histocompatibility complex class I allele Ld was studied . Peptides generated in cells from minigenes coding for peptides of 17-and 19-amino acid length were compared with the in vitro 208 proteasome degradation products of the respective synthetic peptides. The quality o£generated peptides was independent of ubiquitination . In vivo and in vitro processing products were indistinguishable with respect to peptide size and abundance . Altering the neighboring sequence substantially improved the yield of the final antigenic nonapeptide by 20S proteasome cleavage . These results suggest that, in addition to the presence of major histocompatibility complex class I allelic motifs, the cleavage preference ofthe proteasome can define the antigenic potential of a protein . 1865 J. Exp. Med.
2014
The proteasome is responsible for the breakdown of cellular proteins. Proteins targeted for degradation are allowed inside the proteasome particle, where they are cleaved into small peptides and released in the cytosol to be degraded into amino acids. In vertebrates, some of these peptides escape degradation in the cytosol, are loaded onto class I molecules of the major histocompatibility complex (MHC) and displayed at the cell surface for scrutiny by the immune system. The proteasome therefore plays a key role for the immune system: it provides a continued sampling of intracellular proteins, so that CD8-positive T-lymphocytes can kill cells expressing viral or tumoral proteins. Consequently, the repertoire of peptides displayed by MHC class I molecules at the cell surface depends on proteasome activity, which may vary according to the presence of proteasome subtypes and regulators. Besides standard proteasomes, cells may contain immunoproteasomes, intermediate proteasomes and thymoproteasomes. Cells may also contain regulators of proteasome activity, such as the 19S, PA28 and PA200 regulators. Here, we review the effects of these proteasome subtypes and regulators on the production of antigenic peptides. We also discuss an unexpected function of the proteasome discovered through the study of antigenic peptides: its ability to splice peptides.
Proteasome subtypes and the processing of tumor antigens: increasing antigenic diversity
Current Opinion in Immunology, 2012
Protein degradation by the proteasome releases peptides that can be loaded on MHC class I molecules and presented to cytolytic T lymphocytes. Several mechanisms were recently found to increase the diversity of antigenic peptides displayed at the cell surface, thereby maximizing the efficacy of immune responses. The proteasome was shown to produce spliced antigenic peptides, which are made of two fragments initially not contiguous in the parental protein. Different proteasome subtypes also produce distinct sets of antigenic peptides: the standard proteasome and the immunoproteasome, containing different catalytic subunits, have different cleavage specificities and produce different sets of peptides. Moreover, recent work confirmed the existence of two additional proteasome subtypes that are intermediate between the standard and the immunoproteasome, and each produce a unique peptide repertoire.
The Journal of …, 2006
The immunoproteasome (IP) is usually viewed as favoring the production of antigenic peptides presented by MHC class I molecules, mainly because of its higher cleavage activity after hydrophobic residues, referred to as the chymotrypsin-like activity. However, some peptides have been found to be better produced by the standard proteasome. The mechanism of this differential processing has not been described. By studying the processing of three tumor antigenic peptides of clinical interest, we demonstrate that their differential processing mainly results from differences in the efficiency of internal cleavages by the two proteasome types. Peptide gp100 209 -217 (ITDQVPSFV) and peptide tyrosinase 369 -377 (YMDGTMSQV) are destroyed by the IP, which cleaves after an internal hydrophobic residue. Conversely, peptide MAGE-C2 336 -344 (ALKDVEERV) is destroyed by the standard proteasome by internal cleavage after an acidic residue, in line with its higher postacidic activity. These results indicate that the IP may destroy some antigenic peptides due to its higher chymotrypsin-like activity, rather than favor their production. They also suggest that the sets of peptides produced by the two proteasome types differ more than expected. Considering that mature dendritic cells mainly contain IPs, our results have implications for the design of immunotherapy strategies.
2002
The proteasome is now recognized to be implicated in the generation of the vast majority of MHC class I ligands. Moreover, it is probably the only cytosolic protease generating their carboxyterminals. However, solid evidence documents a role of additional and only partly identified proteases in MHC class I antigen processing. Cytosolic tripeptidyl peptidase (TTP II) may be able to carry out some functions normally ascribed to the proteasome, including that of generating antigenic peptides. Several cytosolic enzymes, including bleomycin hydrolase (BH) and puromycin-sensitive aminopeptidase (PSA), but especially the IFNgamma-inducible leucyl aminopeptidase (LAP), can trim the aminoterminal ends of class I ligands. The vast majority of cytosolic peptides is degraded, a process likely to limit antigen presentation, in which thimet oligopeptidase (TOP) may play an important role. Proteolytic activity in the secretory pathway, though much more limited than in the cytosol, also contributes to class I antigen presentation. Signal peptide fragments and peptides at the carboxyterminal end of various proteins targeted to the endoplasmic reticulum can be highly efficient TAP-independent class I ligands. However, an as yet unidentified luminal trimming aminopeptidase may eventually turn out to play the most important role for class I ligand generation in the secretory pathway. Defining the extent of the involvement of cytosolic and luminal peptidases in class I antigen processing will be a challenging task for the future.